Packet transfer apparatus

ABSTRACT

A packet transfer apparatus connects two networks of different protocols. The packet transfer apparatus, connected to a first communication network and a second communication network, performs the steps of: storing first destination correspondence information; receiving a packet of the first communication protocol; based on the first destination correspondence information, determining destination information of a packet of the second communication protocol corresponding to destination information of the received packet of the first communication protocol; generating the header of the packet of the second communication protocol, based on the determined destination information of the packet of the second communication protocol; converting the received one or more packets of the first communication protocol into one or more packets of the third communication protocol; and adding the generated header of the packet of the second communication protocol to the packets of the third communication protocol.

CLAIM OF PRIORITY

This application is a Continuation of U.S. application Ser. No.12/929,100, filed Dec. 30, 2010, which is a Continuation of U.S. patentapplication Ser. No. 12/073,951, filed Mar. 12, 2008 now U.S. Pat. No.7,876,778, issued Jan. 25, 2011). The present application claimspriority from Japanese application JP 2007-180987 filed on Jul. 10,2007, the content of which is hereby incorporated by reference into thisapplication.

FIELD OF THE INVENTION

The present invention relates to a packet transfer apparatus connectedto a first communication network and a second communication network, andmore particularly to technology for converting packet protocols.

BACKGROUND OF THE INVENTION

ATM (Asynchronous Transfer Mode) that performs data communication byusing fixed-length packets (or fixed-length frames) is widely used froman access network of a telecommunications carrier's network to a metroarea network. ATM is a communication technology developed to handlevarious information items such as data, voice, and moving images overone network. In ATM, a fixed-length packet is referred to as an ATMcell.

ATM has standards such as AAL1 and AAL5. AAL1 is a communicationstandard of connection-type and fixed bit rate. AAL1 is primarily usedfor voice communication such as TDM. AAL5 is a communication standard ofconnectionless type and variable bit rate. AAL5 is used for datacommunication of Ethernet (registered trademark, hereinafter the same)and the like.

A method of for encapsulating and decapsulating data is different forAAL1 and AAL5. Therefore, in an ATM access network, an accessaccommodating apparatus that houses a user terminal is required for eachof user's applications. For example, the ATM access network requires anATM accommodating apparatus, an AAL1 accommodating apparatus, and anAAL5 accommodating apparatus.

In JP-A-2004-260238, a packet transfer apparatus that connects LAN andATM is disclosed.

SUMMARY OF THE INVENTION

Although ATM includes high-quality communication functions such as amaintenance function and a band control function, communication devicesare expensive. Therefore, in recent years, a packet switching protocolthat uses variable-length packets for data communication has gonemainstream. Accordingly, there is a demand for technology for replacinga metro area network to which ATM is applied (ATM metro area network) bya metro area network to which the packet switching protocol is applied(packet switching metro area network). However, there has been a problemin that a packet transfer apparatus that connects an ATM access networkand the packet switching metro area network does not exist.

The present invention has been made in view of the aforementionedproblem, and its object is to offer a packet transfer apparatus thatconnects two networks of different protocols.

A typical embodiment of the present invention is a packet transferapparatus connected to a first communication network over which datacommunication is performed with a first communication protocol, and asecond communication network over which data communication is performedwith a second communication protocol. The packet transfer apparatusstores first destination correspondence information containing thecorrespondence between the destination information of packets of thefirst communication protocol and the destination information of packetsof the second communication protocol for transferring packets of thefirst communication protocol to the second communication network. Itreceives a packet of the first communication protocol generated byconversion of a packet of a third communication protocol from the firstcommunication network, and based on the first destination correspondenceinformation, determines destination information of a packet of thesecond communication protocol corresponding to destination informationof the received packet of the first communication protocol. Furthermore,the packet transfer apparatus generates the header of the packet of thesecond communication protocol, based on the determined destinationinformation of the packet of the second communication protocol, convertsthe received one or more packets of the first communication protocolinto one or more packets of the third communication protocol, and addsthe generated header of the packet of the second communication protocolto the packets of the third communication protocol generated by theconversion. Thereby, the packet transfer apparatus converts the packetsgenerated by the conversion into the packet of the second communicationprotocol, and transmits the packet of the second communication protocolgenerated by the conversion to the second communication network.

According to the typical embodiment of the present invention, the packettransfer apparatus can connect two networks of different protocols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the construction of a telecommunicationscarrier's network of an embodiment of the present invention;

FIG. 2 is a block diagram of the construction of a telecommunicationscarrier's network that does not include a packet transfer apparatus;

FIG. 3 is a block diagram of the construction of a packet transferapparatus of an embodiment of the present invention;

FIG. 4 is a drawing showing the structure of an ATM connection tablestored in a packet transfer apparatus of an embodiment of the presentinvention;

FIG. 5 is a drawing showing the structure of an MPLS header conversiontable stored in a packet transfer apparatus of an embodiment of thepresent invention;

FIG. 6 is a drawing showing the structure of an MPLS connection tablestored in a packet transfer apparatus of an embodiment of the presentinvention;

FIG. 7 is a drawing showing the structure of an ATM header conversiontable stored in a packet transfer apparatus of an embodiment of thepresent invention;

FIG. 8 is a block diagram of a functional construction of an ATM accessnetwork accommodated IF provided in a packet transfer apparatus of anembodiment of the present invention;

FIG. 9 is a flowchart of processing of a VPI/VCI connection check andallocation unit of an embodiment of the present invention;

FIG. 10 is a flowchart of processing of an MPLS encapsulating unit of anembodiment of the present invention;

FIG. 11 is a flowchart of MAC automatic learning processing executed bya metro accommodating apparatus shown in FIG. 2;

FIG. 12 is a flowchart of MPLS label determination processing executedby the metro accommodating apparatus shown in FIG. 2;

FIG. 13 is a flowchart of processing of an MPLS decapsulating andallocation unit of a first embodiment of the present invention;

FIG. 14 is a flowchart of processing of an ATM header generating unit ofan embodiment of the present invention;

FIG. 15 is an explanatory drawing of protocol stack of communicationconcerning TDM frame of an embodiment of the present invention;

FIG. 16 is an explanatory drawing of protocol stack of communicationconcerning TDM frame in a telecommunications carrier's networkconstructed as shown in FIG. 2;

FIG. 17 is an explanatory drawing of protocol stack of communicationconcerning Ethernet frame of an embodiment of the present invention;

FIG. 18 is an explanatory drawing of communication concerning Ethernetframe of an embodiment of the present invention;

FIG. 19 is an explanatory drawing of protocol stack of communicationconcerning Ethernet frame in a telecommunications carrier's networkconstructed as shown in FIG. 2; and

FIG. 20 is an explanatory drawing of communication concerning Ethernetframe in a telecommunications carrier's network constructed as shown inFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

This embodiment assumes that a first communication protocol is ATM(Asynchronous Transfer Mode), and a second communication protocol isMPLS. However, the first communication protocol may not be ATM but maybe any communication protocol of connection type. The secondcommunication protocol may not be MPLS but may be any communicationprotocol of connection type. However, the second communication protocolis preferably a packet switching protocol that allowsconnection-oriented bus setting and high-quality communication. Packetsin the claims include cells and frames.

FIG. 1 is a block diagram of the construction of a telecommunicationscarrier's network of an embodiment of the present invention.

The telecommunications carrier's network includes user terminals 1, 2,and 3, ATM access network 10, packet transfer apparatus 100, packetswitching metro area network 30, packet transfer apparatus 11, ATM relaynetwork 12A, and TDM relay network 12B, and IP/Ethernet relay network12C.

The ATM access network 10 includes ATM accommodating apparatuses 4A1 and4A2, AAL1 accommodating apparatus 4B1, and AAL5 accommodating apparatus4C1.

The ATM accommodating apparatus 4A1 is a device that houses a userterminal 1. The user terminal 1 transmits and receives ATM cells. TheATM accommodating apparatus 4A2 is a device connected to the packettransfer apparatus 100.

The ATM accommodating apparatuses 4A1 and 4A2 receive an ATM cell. Then,the ATM accommodating apparatuses 4A1 and 4A2 determine a transferdestination of the ATM cell, based on the ATM header of the received ATMcell. Next, the ATM accommodating apparatuses 4A1 and 4A2 transfer thereceived ATM cell to the determined transfer destination.

The AAL1 accommodating apparatus 4B1 is a device that houses a userterminal 2. The user terminal 2 performs TDM communication such as aphone or PBX.

The AAL1 accommodating apparatus 4B1 receives a TDM frame from the userterminal 2. Next, the AAL1 accommodating apparatus 4B1 transforms thereceived TDM frame into a capsule in AAL1 format. Thereby, the AAL1accommodating apparatus 4B1 converts the received TDM frame into an AAL1frame.

Next, the AAL1 accommodating apparatus 4B1 splits the AAL1 framegenerated by the conversion into ATM cell size, and adds an ATM header.Thereby, the AAL1 accommodating apparatus 4B1 converts the AAL1 frameinto an ATM cell. AAL1 accommodating apparatus 4B1 transmits the ATMcell generated by the conversion to the ATM access network 10.

The AAL1 accommodating apparatus 4B1 receives an ATM cell from the ATMaccess network 10. Then, AAL1 accommodating apparatus 4B1 converts oneor more received ATM cells into an AAL1 frame. Next, the AAL1accommodating apparatus 4B1 decapsulates the AAL1 frame generated by theconversion. Thereby, the AAL1 accommodating apparatus 4B1 converts theAAL1 frame into a TDM frame. The AAL1 accommodating apparatus 4B1transmits the TDM frame generated by the conversion to the user terminal2.

The AAL5 accommodating apparatus 4C1 is a device that houses a userterminal 3. The user terminal 3 performs Ethernet communication.

The AAL5 accommodating apparatus 4C1 receives an Ethernet frame from theuser terminal 3. Next, the AAL5 accommodating apparatus 4C1 decapsulatesthe received Ethernet frame in AAL5 format. Thereby, the AAL5accommodating apparatus 4C1 converts the received Ethernet frame into anAAL5 frame.

Next, the AAL5 accommodating apparatus 4C1 splits the AAL5 framegenerated by the conversion into ATM cell size, and adds an ATM header.Thereby, the AAL5 accommodating apparatus 4C1 converts the AAL5 frameinto an ATM cell. The AAL5 accommodating apparatus 4C1 transmits the ATMcell generated by the conversion to the ATM access network 10.

The AAL5 accommodating apparatus 4C1 receives an ATM cell from the ATMaccess network 10. Then, AAL5 accommodating apparatus 4C1 converts oneor more received ATM cells into an AAL5 frame. Next, the AAL5accommodating apparatus 4C1 decapsulates the AAL5 frame generated by theconversion. Thereby, the AAL5 accommodating apparatus 4C1 converts theAAL5 frame into an Ethernet frame. The AAL5 accommodating apparatus 4C1transmits the Ethernet frame generated by the conversion to the userterminal 2.

The packet transfer apparatus 100 connects the packet switching metroarea network 30 and the ATM access network 10. The packet transferapparatus 100 will be detailed in FIG. 3.

The packet transfer apparatus 11 connects the packet switching metroarea network 30, the ATM relay network 12A, the TDM relay network 12B,and the IP/Ethernet relay network 12C.

In the packet switching metro area network 30, MPLS packets are used fordata communication.

In the ATM relay network 12A, ATM cells are used for data communication.The ATM relay network 12A includes an ATM accommodating apparatus 4A3.The ATM accommodating apparatus 4A3 has the same functions as the ATMaccommodating apparatuses 4A1 and 4A2.

In the TDM relay network 12B, TDM frames are used for datacommunication. The TDM relay network 12B includes an AAL1 accommodatingapparatus 4B3. The AAL1 accommodating apparatus 4B3 has the samefunctions as the AAL1 accommodating apparatus 4B1.

In the IP/Ethernet relay network 12C, Ethernet frames are used for datacommunication. The IP/Ethernet relay network 12C includes an AAL5accommodating apparatus 4C3. The AAL5 accommodating apparatus 4C3 hasthe same functions as the AAL5 accommodating apparatus 4C1.

The packet transfer apparatus 11 includes an MPLS metro interface (IF)9A, an ATM accommodating IF 8A2, a TDM accommodating IF 8B2, and anEthernet accommodating IF 8C2.

The MPLS metro IF 9A is an interface connected with the packet switchingmetro area network 30.

The ATM accommodating IF 8A2 is an interface connected to the ATM relaynetwork 12A. The ATM accommodating IF 8A2 mutually converts MPLS packetsand ATM cells.

The TDM accommodating IF 8B2 is an interface connected to the TDM relaynetwork 12B. The TDM accommodating IF 8B2 mutually converts MPLS packetsand TDM frames.

The Ethernet accommodating IF 8C2 is an interface connected to theIP/Ethernet relay network 12C. The Ethernet accommodating IF 8C2mutually converts MPLS packets and Ethernet frames.

The following describes the telecommunications carrier's network whenthe ATM metro area network is replaced by the packet switching metroarea network, without providing the packet transfer apparatus 100 ofthis embodiment.

FIG. 2 is a block diagram showing the construction of thetelecommunications carrier's network when the packet transfer apparatus100 is not provided.

The telecommunications carrier's network not including the packettransfer apparatus 100 of this embodiment includes the metroaccommodating apparatuses 5A, 5B, and 5C in place of the packet transferapparatus 100. Therefore, the ATM access network 10 of thetelecommunications carrier's network not including the packet transferapparatus 100 further must include an AAL1 accommodating apparatus 4B2and an AAL5 accommodating apparatus 4C2. Other components of thetelecommunications carrier's network not including the packet transferapparatus 100 are the same as the components (FIG. 1) of thetelecommunications carrier's network of this embodiment. The samecomponents are identified by the same reference numerals; descriptionsof them are not omitted.

The metro accommodating apparatuses 5A, 5B, and 5 C connect the packetswitching metro area network 30 and the ATM access network 10.

The metro accommodating apparatus 5A includes an ATM accommodating IF8A1 and an MPLS metro IF 9A. The ATM accommodating IF 8A1 is aninterface connected to the ATM accommodating apparatus 4A2. The ATMaccommodating IF 8A1 mutually converts MPLS packets and ATM cells.

The MPLS metro IF 9A is an interface connected to the packet switchingmetro area network 30.

The metro accommodating apparatus 5B includes a TDM accommodating IF 8B1and an MPLS metro IF 9A. The TDM accommodating IF 8B1 is an interfaceconnected to AAL1 accommodating apparatus 4B2. The TDM accommodating IF8B1 mutually converts MPLS packets and TDM frames.

The metro accommodating apparatus 5C includes an Ethernet accommodatingIF 8C1 and the MPLS metro IF 9A. The Ethernet accommodating IF 8C1 is aninterface connected to the AAL5 accommodating apparatus 4C2. TheEthernet accommodating IF 8C1 mutually converts MPLS packets andEthernet frames.

The AAL1 accommodating apparatus 4B2 is a device connected to the metroaccommodating apparatus 5B. The AAL1 accommodating apparatus 4B2 has thesame functions as the AAL1 accommodating apparatus 4B1.

The AAL1 accommodating apparatus 4B2 receives a TDM frame from the metroaccommodating apparatus 5B. Next, the AAL1 accommodating apparatus 4B2encapsulates the received TDM frame in AAL1 format. Thereby, the AAL1accommodating apparatus 4B2 converts the received TDM frame into theAAL1 frame.

Next, the AAL1 accommodating apparatus 4B2 splits the AAL1 framegenerated by conversion into ATM cell size, and adds an ATM header.Thereby, the AAL1 accommodating apparatus 4B2 converts the AAL1 frameinto an ATM cell. The AAL1 accommodating apparatus 4B2 transmits the ATMcell generated by the conversion to the ATM access network 10.

The AAL1 accommodating apparatus 4B2 receives an ATM cell from the ATMaccess network 10. Then, AAL1 accommodating apparatus 4B2 converts oneor more received ATM cells into the AAL1 frame. Next, the AAL1accommodating apparatus 4B2 decapsulates the AAL1 frame generated by theconversion. Thereby, the AAL1 accommodating apparatus 4B2 converts theAAL1 frame into a TDM frame. The AAL1 accommodating apparatus 4B2transmits the TDM frame generated by the conversion to the metroaccommodating apparatus 5B.

The AAL5 accommodating apparatus 4C2 is a device connected to the metroaccommodating apparatus 5C. The AAL5 accommodating apparatus 4C2 has thesame functions as the AAL5 accommodating apparatus 4C1.

The AAL5 accommodating apparatus 4C2 receives an Ethernet frame from themetro accommodating apparatus 5C. Next, the AAL5 accommodating apparatus4C2 encapsulates the received Ethernet frame in AAL5 format. Thereby,the AAL5 accommodating apparatus 4C2 converts the received Ethernetframe into an AAL5 frame.

Next, the AAL5 accommodating apparatus 4C2 splits the AAL5 framegenerated by the conversion into ATM cell size, and adds an ATM header.Thereby, the AAL5 accommodating apparatus 4C2 converts the AAL5 frameinto an ATM cell. The AAL5 accommodating apparatus 4C2 transmits the ATMcell generated by the conversion to the ATM access network 10.

The AAL5 accommodating apparatus 4C2 receives an ATM cell from the ATMaccess network 10. Then, the AAL5 accommodating apparatus 4C2 convertsone or more received ATM cells into an AAL5 frame. Next, the AAL5accommodating apparatus 4C2 decapsulates the AAL5 frame generated by theconversion. Thereby, the AAL5 accommodating apparatus 4C2 converts theAAL5 frame into an Ethernet frame. The AAL5 accommodating apparatus 4C2transmits an Ethernet frame generated by the conversion to the metroaccommodating apparatus 5C.

FIG. 3 is a block diagram showing the construction of the packettransfer apparatus 100 of an embodiment of the present invention.

The packet transfer apparatus 100 includes tributary IF accommodatingslot 33, ATM access network accommodated IF 31, up-link IF accommodatingslot 34, MPLS metro IF 9A, switch 32, and control unit 35.

The tributary IF accommodating slot 33 houses an interface connected tothe ATM access network 10, the ATM relay network 12A, the TDM relaynetwork 12B, or the IP/Ethernet relay network 12C. For example, thetributary IF accommodating slot 33 houses one or more ATM access networkaccommodated IFs 31. The tributary IF accommodating slot 33 may houseATM accommodating IF, TDM accommodating IF, Ethernet accommodating IF,or the like.

The ATM access network accommodated IF 31 is an interface connected tothe ATM access network 10. The ATM access network accommodated IF 31stores various tables including ATM connection table 43 (FIG. 4), MPLSheader conversion table 47 (FIG. 5), MPLS connection table 53 (FIG. 6),ATM header conversion table 57 (FIG. 7). The ATM access networkaccommodated IF 31 will be detailed in FIG. 8.

The ATM accommodating IF is an interface connected to the ATM relaynetwork 12A. The ATM accommodating IF mutually converts MPLS packets andATM cells.

The TDM accommodating IF is an interface connected to the TDM relaynetwork 12B. Moreover, it mutually converts MPLS packets and TDM frames.

The Ethernet accommodating IF is an interface connected to theIP/Ethernet relay network 12C. Moreover, it mutually converts MPLSpackets and Ethernet frames.

The up-link IF accommodating slot 34 houses one or more MPLS metro IFs9A. The MPLS metro IF 9A is an interface connected to the packetswitching metro area network 30.

The switch 32 controls transfer of MPLS packets between IFs includingthe ATM access network accommodated IF 31, the MPLS metro IF 9A, and thelike.

The control unit 35 controls processing of the ATM access networkaccommodated IF 31, the MPLS metro IF 9A, and the switch 32. Moreover,it receives information from an external management terminal (not shownin the drawing), and based on the received information, updates varioustables stored in the ATM access network accommodated IF 31.

FIG. 4 is a block diagram of the ATM connection table 43 stored in thepacket transfer apparatus 100 of the embodiment of the presentinvention.

The ATM connection table 43 includes VPI (Virtual Path Identifier) 61,VCI (Virtual Channel Identifier) 62, connection ID 63, and upper layercommunication protocol type 64.

The VPI 61 and the VCI 62 are identifiers showing the destination of anATM cell received by the ATM access network accommodated IF 31.

The connection ID 63 is a unique identifier of connection correspondingto an ATM cell pertinent to a relevant record. The connection ID 63 isadded to an ATM cell pertinent to a relevant record. The upper layercommunication protocol type 64 shows the type of a communicationprotocol of an upper layer of an ATM cell pertinent to a relevantrecord. In this embodiment, the upper communication protocol 64 showsany of ATM bearer, AAL1, or AAL5.

FIG. 5 is a drawing showing the structure of an MPLS header conversiontable 47 stored in the packet transfer apparatus 100 of an embodiment ofthe present invention.

The MPLS header conversion table 47 includes connection IDs 65, tunnellabel values 66, and VC label values 67.

The connection ID 65 is a unique identifier of connection. The tunnellabel value 66 and the VC label value 67 are an identifier showing thedestination of an MPLS packet corresponding to connection identified byconnection ID 65 of a relevant record.

Although an MPLS packet of this embodiment has two MPLS labels, tunnellabel and VC label, it may have any number of MPLS labels.

FIG. 6 is a drawing showing the structure of the MPLS connection table53 stored in the packet transfer apparatus 100 of an embodiment of thepresent invention.

The MPLS connection table 53 includes tunnel label value 71, VC labelvalue 72, connection ID 73, and upper layer communication protocol type74.

The tunnel label value 71 and the VC label value 72 are an identifiershowing the destination of an MPLS packet received by the ATM accessnetwork accommodated IF 31.

The connection ID 73 is a unique identifier of connection correspondingto an MPLS packet pertinent to a relevant record. The connection ID 73is added to an MPLS packet pertinent to a relevant record. The upperlayer communication protocol type 74 shows the type of a communicationprotocol of an upper layer of an ATM cell generated from an MPLS packetpertinent to a relevant record.

FIG. 7 is a drawing showing the structure of an ATM header conversiontable 57 stored in the packet transfer apparatus 100 of an embodiment ofthe present invention.

The ATM header conversion table 57 includes connection ID 75, VPI 76,and VCI 77.

The connection ID 75 is a unique identifier of connection. VPI 76 andVCI 77 are identifiers showing the destination of an ATM cellcorresponding to connection identified by the connection ID 75 of arelevant record.

FIG. 8 is a block diagram of a functional construction of the ATM accessnetwork accommodated IF 31 provided in the packet transfer apparatus 100of an embodiment of the present invention.

The ATM access network accommodated IF 31 includes an input processingunit, an output processing unit, and a control unit communication IF 40.

The control unit communication IF 40 is an interface for communicatingwith the control unit 35. For example, the control unit communication IF40 transmits commands received from the control unit 35 to eachprocessing unit.

On receiving an ATM cell from the ATM access network 10, the inputprocessing unit converts the received ATM cell into an MPLS packet. Theinput processing unit transmits the MPLS packet generated by theconversion to the switch 32.

The input processing unit includes ATM cell receiving unit 41, VPI(Virtual Path Identifier)/VCI (Virtual Channel Identifier) connectioncheck and allocation unit 42, ATM connection table 43, ATM bearerterminal 44A, and AAL1 terminal 44B, AAL5 terminal 44C, scheduler 45S,MPLS encapsulating unit 46, MPLS header conversion table 47, and switchpacket transmitting unit 48.

The ATM cell receiving unit 41 receives the ATM cell from the ATM accessnetwork 10. Then, it determines whether the received ATM cell is normal,based on the ATM header of the received ATM cell. When the ATM cell isabnormal, it discards the received ATM cell. On the other hand, when theATM cell is normal, it transmits the received ATM cell to the VPI/VCIconnection check and allocation unit 42.

The VPI/VCI connection check and allocation unit 42 receives an ATM cellfrom ATM cell receiving unit 41. Then, it consults the ATM connectiontable 43 to determine an upper layer communication protocol type andconnection of the received ATM cell. Processing of the VPI/VCIconnection check and allocation unit 42 will be detailed in FIG. 9.

The ATM bearer terminal 44A receives an ATM cell added with a connectionID from the VPI/VCI connection check and allocation unit 42. Then, ittemporarily stores the received ATM cell in a cell buffer. It transmitsa read request to the scheduler 45.

On receiving a read permission notice from the scheduler 45, the ATMbearer terminal 44A transmits one ATM cell stored in the cell buffer tothe scheduler 45.

The AAL1 terminal 44B receives an ATM cell added with a connection IDfrom the VPI/VCI connection check and allocation unit 42. Then, itclassifies the received ATM cell by connection ID added to the receivedATM cell.

Next, the AAL1 terminal 44B converts the classified ATM cell into a TDMframe.

Specifically, the AAL1 terminal 44B converts one or more ATM cells addedwith an identical session ID into an AAL1 frame. Next, it decapsulatesthe AAL1 frame generated by the conversion. Thereby, the AAL1 terminal44B converts the AAL1 frame into a TDM frame.

Next, the AAL1 terminal 44B stores the TDM frame generated by theconversion in a frame buffer. It transmits a read request to thescheduler 45.

On receiving a read permission notice from the scheduler 45, the AAL1terminal 44B, to the start of one TDM frame stored in the frame buffer,adds a connection ID added to an ATM cell having been converted into theTDM frame. Then, it transmits the TDM frame added with the connection IDto the scheduler 45.

The AAL5 terminal 44C receives an ATM cell added with a connection IDfrom the VPI/VCI connection check and allocation unit 42. Then, itclassifies the received ATM cell by connection ID added to the receivedATM cell.

Next, the AAL5 terminal 44C converts the classified ATM cell into anEthernet frame.

Specifically, the AAL5 terminal 44C converts one or more ATM cells addedwith an identical session ID into an AAL5 frame. The ATM header of anATM cell contains bits indicating a relative position of the ATM cell inan AAL5 frame. Accordingly, the AAL5 terminal 44C refers to the bitscontained in the ATM header of an ATM cell to convert one or more ATMcells into an AAL5 frame.

Next, the AAL5 terminal 44C decapsulates the AAL5 frame generated by theconversion. Thereby, the AAL5 terminal 44C converts the AAL5 frame intoan Ethernet frame.

Next, the AAL5 terminal 44C stores the Ethernet frame generated by theconversion in the frame buffer. The AAL5 terminal 44 c transmits a readrequest to the scheduler 45.

On receiving a read permission notice from the scheduler 45, the AAL5terminal 44C, to the start of one Ethernet frame stored in the framebuffer, adds a connection ID added to an ATM cell having been convertedinto the Ethernet frame. Then, it transmits the TDM frame added with theconnection ID to the scheduler 45.

The scheduler 45 receives a read request from at least one of the ATMbearer terminal 44A, the AAL1 terminal 44B, and the AAL5 terminal 44C.Then, the scheduler 45 determines a terminal permitted to read data fromamong the ATM bearer terminal 44A, the AAL1 terminal 44B, and the AAL5terminal 44C that have transmitted the received read request. Thescheduler 45 transmits a read permission notice to the determinedterminal.

At this time, the scheduler 45 preferentially determines the AAL1terminal 44B as a terminal permitted to read data. This is because AAL1frames are used in communication that requires real time capability suchas voice communication. Thereby, one ATM access network accommodated IF31 can support three types of upper communication protocols the ATMbearer, AAL1, and AAL5 while minimizing processing delay of AAL1 frames.

After that, the scheduler 45 receives an ATM cell, TDM frame, orEthernet frame from the terminal to which the read permission notice istransmitted. The scheduler 45 transmits, the received ATM cell, TDMframe or Ethernet frame to the MPLS encapsulating unit 46.

The MPLS encapsulating unit 46 receives an ATM cell, TDM frame, orEthernet frame from the scheduler 45. Then, it consults the MPLS headerconversion table 47 to determine an MPLS label. It encapsulates thereceived ATM cell, TDM frame or Ethernet frame with the determined MPLSlabel. Standard of encapsulating ATM cells with MPLS label, standard ofencapsulating TDM frames with MPLS label, and standard of encapsulatingEthernet frames with MPLS label are stipulated by standardizationgroups.

Thereby, the MPLS encapsulating unit 46 converts the received ATM cell,TDM frame, or Ethernet frame into an MPLS packet. Processing of the MPLSencapsulating unit 46 will be detailed in FIG. 10.

The switch packet transmitting unit 48 receives the MPLS packet from theMPLS encapsulating unit 46. Then, it transfers the received MPLS packetto the switch 32.

On receiving the MPLS packet from the switch 32, the output processingunit converts the received MPLS packet into an ATM cell. Then, ittransmits an MPLS packet generated by the conversion to the ATM accessnetwork 10.

The output processing unit includes a switch packet receiving unit 51,an MPLS decapsulating and allocation unit 52, an MPLS connection table53, an ATM bearer generating unit 54A, an AAL1 generating unit 54B, anAAL5 generating unit 54C, a scheduler 55, an ATM header generating unit56, an ATM header conversion table 57, and an ATM cell transmitting unit58.

The switch packet receiving unit 51 receives the MPLS packet from theswitch. Then, it determines whether the received MPLS packet is normal.When the MPLS packet abnormal, it discards the received MPLS packet. Onthe other hand, when the MPLS packet is normal, it transmits thereceived MPLS packet to the MPLS decapsulating and allocation unit 52.

The MPLS decapsulating and allocation unit 52 receives the MPLS packetfrom the switch packet receiving unit 51. Then, it consults the MPLSconnection table 53 to determine an upper layer communication protocoltype and connection of the received MPLS packet. Processing of the MPLSdecapsulating and allocation unit 52 will be detailed in FIG. 13.

The ATM bearer generating unit 54A receives the payload of an ATM celladded with a connection ID from the MPLS decapsulating and allocationunit 52. Then, it temporarily stores the payload of the received ATMcell in the cell buffer. It transmits a read request to the scheduler55.

On receiving a read permission notice from the scheduler 55, the ATMbearer generating unit 54A transmits the payload of one ATM cell storedin the cell buffer to the scheduler 55.

The AAL1 generating unit 54B receives a TDM frame added with aconnection ID from the MPLS decapsulating and allocation unit 52. Then,it removes the connection ID from the received TDM frame. Next, itencapsulates the TDM frame with the connection ID removed in AAL1format. Thereby, it converts the TDM frame with the connection IDremoved into an AAL1 frame.

Next, the AAL1 generating unit 54B splits the AAL1 frame generated bythe conversion into the size of the payload of ATM cell. When the sizeof the split data is less than the payload size of ATM cell, the AAL1generating unit 54B performs padding processing.

Thereby, the AAL1 generating unit 54B converts the AAL1 frame into thepayload of ATM cell. Next, it temporarily stores the payload of ATM cellgenerated by the conversion in the cell buffer. It transmits a readrequest to the scheduler 55.

On receiving a read permission notice from the scheduler 55, the AAL1generating unit 54B, to the start of the payload of one ATM cell storedin the cell buffer, adds a connection ID removed from the TDM frameconverted into the payload of the ATM cell. It transmits the payload ofthe ATM cell added with a connection ID to the scheduler 55.

The AAL5 generating unit 54C receives an Ethernet frame added with aconnection ID from the MPLS decapsulating and allocation unit 52. Then,it removes the connection ID from the received Ethernet frame. Next, itencapsulates the Ethernet frame with the connection ID removed, in AAL5format. Thereby, it converts the Ethernet frame with the connection IDremoved into an AAL5 frame.

Next, the AAL5 generating unit 54C splits the AAL5 frame generated bythe conversion into the payload size of ATM cell. Thereby, it convertsthe AAL5 frame into the payload of ATM cell.

Next, the AAL5 generating unit 54C temporarily stores the payload of ATMcell generated by the conversion in the cell buffer. It transmits a readrequest to the scheduler 55.

On receiving a read permission notice from the scheduler 55, the AAL5generating unit 54C, to the start of the payload of one ATM cell storedin the cell buffer, adds a connection ID removed from an Ethernet frameconverted into the payload of the ATM cell. It transmits the payload ofATM cell with the connection ID added to the scheduler 55.

The scheduler 55 receives a read request from at least one of the ATMbearer generating unit 54A, the AAL1 generating unit 54B, and the AAL5generating unit 54C. Then, it determines a generating unit permitted toread data from among the ATM bearer generating unit 54A, the AAL1generating unit 54B, and the AAL5 generating unit 54C that havetransmitted the received read request. It transmits a read permissionnotice to the determined generating unit.

At this time, the scheduler 55 preferentially determines the AAL1generating unit 54B as a generating unit permitted to read data. This isbecause AAL1 frames are used in communication that requires real timecapability such as voice communication. Thereby, one ATM access networkaccommodated IF 31 can support three types of upper communicationprotocols the ATM bearer, AAL1, and AAL5 while minimizing processingdelay of AAL1 frames.

After that, the scheduler 55 receives the payload of ATM cell from thegenerating unit to which the read permission notice is transmitted. Thescheduler 55 transmits the received payload of ATM cell to the ATMheader generating unit 56.

The ATM header generating unit 56 receives the payload of ATM cell fromthe scheduler 55. It consults the ATM header conversion table 57 tocreate an ATM header. It adds the generated ATM header to the receivedpayload of ATM cell. Thereby, it creates an ATM cell. Processing of theATM header generating unit 56 will be detailed in FIG. 14.

The ATM cell transmitting unit 58 receives an ATM cell from the ATMheader generating unit 56. Then, it transmits the received ATM cell tothe ATM access network 10.

The packet transfer apparatus 100 of this embodiment includes an ATMaccess network accommodated IF 31 constructed as described above.Thereby, a metro area network of a telecommunications carrier's networkto which ATM protocol is applied can be replaced by a packet switchingmetro area network to which MPLS protocol is applied.

FIG. 9 is a flowchart of processing of the VPI/VCI connection check andallocation unit 42 of an embodiment of the present, invention.

The VPI/VCI connection check and allocation unit 42, when receiving anATM cell from the ATM cell receiving unit 41, performs relevantprocessing.

First, the VPI/VCI connection check and allocation unit 42 selects arecord corresponding to the received ATM cell from the ATM connectiontable 43 (S171).

Specifically, the VPI/VCI connection check and allocation unit 42extracts VPI and VCI from the ATM header of the received ATM cell. Next,it selects a record that has VPI 61 of the ATM connection table 43matching the extracted VPI and VCI 62 of the ATM connection table 43matching the extracted VCI, from the ATM connection table 43.

Next, it determines whether a record corresponding to the received ATMcell has been selected from the ATM connection table 43 (S172).

When a record corresponding to the received ATM cell has not beenselected, the VPI/VCI connection check and allocation unit 42 discardsthe received ATM cell (S175). It terminates the processing.

On the other hand, when a record corresponding to the received ATM cellhas been selected, the VPI/VCI connection check and allocation unit 42extracts a connection ID 63 and an upper layer communication protocoltype 64 from the selected record (S173).

Next, the VPI/VCI connection check and allocation unit 42 adds theextracted connection ID 63 to the start of the received ATM cell.

Next, it determines a terminal corresponding to the extracted upperlayer communication protocol type 64 from among the ATM bearer terminal44A, the AAL1 terminal 44B, and the AAL5 terminal 44C.

For example, when the extracted upper layer communication protocol type64 indicates “ATM bearer,” the VPI/VCI connection check and allocationunit 42 determines the ATM bearer terminal 44A. When the extracted upperlayer communication protocol type 64 indicates “AAL1,” it determines theAAL1 terminal 44B. When the extracted upper layer communication protocoltype 64 indicates “AAL5,” it determines the AAL5 terminal 44C.

Next, the VPI/VCI connection check and allocation unit 42 transmits anATM cell added with a connection ID 63 to the determined terminal(S174). Then, it terminates the processing.

As described above, the VPI/VCI connection check and allocation unit 42,based on the VPI and VCI of the received ATM cell, determines thetransfer destination of the received ATM cell from among the ATM bearerterminal 44A, the AAL1 terminal 44B, and the AAL5 terminal 44C.Therefore, one ATM access network accommodated IF 31 can support threetypes of upper communication protocols the ATM bearer, AAL1, and AAL5.

FIG. 10 is a flowchart of processing of the MPLS encapsulating unit 46of an embodiment of the present invention.

On receiving an ATM cell, TDM frame or Ethernet frame from the scheduler45, the MPLS encapsulating unit 46 performs relevant processing.

First, the MPLS encapsulating unit 46 extracts a connection ID from thereceived ATM cell, TDM frame or Ethernet frame. Next, it selects arecord having a connection ID 65 matching the extracted connection IDfrom the MPLS header conversion table 47 (S181).

Next, it extracts a tunnel label value 66 and a VC label value 67 fromthe selected record (S182).

Next, it creates an MPLS label, based on the extracted tunnel labelvalue 66. Next, it generates a VC MPLS label, based on the extracted VClabel value 67.

Next, it encapsulates the received ATM cell, TDM frame, or Ethernetframe by the generated tunnel MPLS label and VC MPLS label (S183). Thetunnel MPLS label and VC MPLS label are added to the start of thereceived ATM cell, TDM frame, or Ethernet frame so that the VC MPLSlabel is inside, and the tunnel MPLS label is outside.

Thereby, the MPLS encapsulating unit 46 converts the received ATM cell,TDM frame, or Ethernet frame into an MPLS packet (S183).

Next, it transmits the MPLS packet generated by the conversion to theswitch packet transmitting unit 48. Then, it terminates the processing.

Thus, it determines an MPLS label, based on the connection ID added tothe received TDM frame or Ethernet frame instead of informationcontained in the received TDM frame or Ethernet frame. The connection IDis uniquely decided by VPI and VCI contained in the ATM header of theATM cell converted into the TDM frame or Ethernet frame. However, theconnection ID may be uniquely determined from only VPI contained in theATM header of the ATM cell instead of the VPI and VCI contained in theATM header of the ATM cell.

Therefore, the ATM access network accommodated IF 31, unlike the metroaccommodating apparatus 5B shown in FIG. 2, does not need to store atime slot—MPLS label correspondence table. The time slot—MPLS labelcorrespondence table is a table for searching for an MPLS label forencapsulating a relevant TDM frame from the time slot of the TDM frame.Therefore, the time slot-MPLS label correspondence table shows thecorrespondence between the time slots of TDM frames and the identifiersof MPLS labels.

The ATM access network accommodated IF 31, unlike the metroaccommodating apparatus 5C shown in FIG. 2, does not need to store a MACaddress—MPLS label correspondence table. The MAC address—MPLS labelcorrespondence table is a table for searching for an MPLS label forencapsulating an Ethernet frame from the destination MAC address of anEthernet frame. Therefore, the MAC address—MPLS label correspondencetable shows the correspondence between MAC addresses and the identifiersof MPLS labels.

A MAC address is an address allocated when a network interface card ofthe user terminal 3 is manufactured. Therefore, it is difficult for amanager of the packet switching metro area network 30 to create the MACaddress—MPLS label correspondence table. Accordingly, the metroaccommodating apparatus 5 c automatically learns the correspondencebetween MAC addresses and MPLS labels by performing MAC automaticlearning processing. Thereby, the metro accommodating apparatus 5Cautomatically creates the MAC address—MPLS label correspondence table.MAC automatic learning processing executed by the metro accommodatingapparatus 5C will be detailed in FIG. 11.

The Metro accommodating apparatus 5C determines an MPLS label forencapsulating an Ethernet frame, based on the MAC address—MPLS labelcorrespondence table. However, the metro accommodating apparatus 5Ccannot determine an MPLS label, it must execute flooding processing.MPLS label determination processing executed by the metro accommodatingapparatus 5C will be detailed in FIG. 12.

On the other hand, the ATM access network accommodated IF of thisembodiment 31 determines an MPLS label, based on a connection ID addedto a received Ethernet frame. Therefore, the ATM access networkaccommodated IF 31, unlike the metro accommodating apparatus 5C shown inFIG. 2, does not need to execute the MAC automatic learning processing.Moreover, the ATM access network accommodated IF 31, unlike the metroaccommodating apparatus 5C shown in FIG. 2, does not need to executeflooding processing.

FIG. 11 is a flowchart of MAC automatic learning processing executed bythe metro accommodating apparatus 5C shown in FIG. 2.

On receiving an MPLS packet from the packet switching metro area network30, the metro accommodating apparatus 5C executes pertinent MACautomatic learning processing.

First, the metro accommodating apparatus 5C decapsulates the receivedMPLS packet. Thereby, the metro accommodating apparatus 5C converts thereceived MPLS packet into an Ethernet frame.

Next, the metro accommodating apparatus 5C extracts a sender MAC addressfrom the Ethernet frame generated by the conversion (S101). Next, themetro accommodating apparatus 5C determines whether a record having aMAC address matching the extracted sender MAC address exists in the MACaddress—MPLS label correspondence table (S102).

When the relevant record exists in the MAC address—MPLS labelcorrespondence table, the metro accommodating apparatus 5C immediatelyterminates the MAC automatic learning processing.

On the other hand, when a relevant record does not exist in the MACaddress—MPLS label correspondence table, the metro accommodatingapparatus 5C adds a new record to the MAC address—MPLS labelcorrespondence table. Next, the metro accommodating apparatus 5C storesthe correspondence between the extracted sender MAC address and theidentifier of the MPLS label of the received MPLS packet in the newrecord (S103). Then, the metro accommodating apparatus 5C terminates theMAC automatic learning processing.

FIG. 12 is a flowchart of MPLS label determination processing executedby the metro accommodating apparatus 5C shown in FIG. 2.

On receiving an Ethernet frame the ATM access network 10, the metroaccommodating apparatus 5C executes the relevant MPLS labeldetermination processing.

First, the metro accommodating apparatus 5C extracts a destination MACaddress from the received Ethernet frame (S111).

Next, the metro accommodating apparatus 5C determines whether a recordhaving a MAC address matching the extracted destination MAC addressexists in the MAC address—MPLS label correspondence table (S112).

When the relevant record exists in the MAC address—MPLS labelcorrespondence table, the metro accommodating apparatus 5C extracts arecord having a MAC address matching the extracted MAC address from theMAC address—MPLS label correspondence table. Next, the metroaccommodating apparatus 5C extracts the identifier of MPLS label fromthe selected record. Next, the metro accommodating apparatus 5C acquiresan MPLS label identified by the extracted identifier.

Next, the metro accommodating apparatus 5C encapsulates the receivedEthernet frame with the acquired MPLS label. Thereby, the metroaccommodating apparatus 5C converts the received Ethernet frame into anMPLS packet.

Next, the metro accommodating apparatus 5C transmits an MPLS packetgenerated by the conversion into an MPLS tunnel (S113). The metroaccommodating apparatus 5C terminates the relevant MPLS labeldetermination processing.

On the other hand, when a relevant record does not exist in the MACaddress—MPLS label correspondence table, it performs flooding processing(S114).

Specifically, the metro accommodating apparatus 5C acquires all MPLSlabels managed by the metro accommodating apparatus 5C. Next, itreproduces as many received Ethernet frames as there are all acquiredMPLS labels.

Next, it encapsulates the reproduced Ethernet frames with each of theall acquired MPLS labels. Thereby, it converts each of the reproducedEthernet frames into an MPLS packet having a different destination.

Next, it transmits the MPLS packet generated by the conversion to theMPLS tunnel. In short, the metro accommodating apparatus 5C transmitsthe MPLS packet to all destinations managed by it. Then, it terminatesthe MPLS label determination processing.

In the flooding processing, the metro accommodating apparatus 5C mustreproduce plural Ethernet frames. Unnecessary MPLS packets will betransmitted to the packet switching metro area network 30. As a result,the metro accommodating apparatus 5C and the packet switching metro areanetwork 30 have been heavily loaded.

On the other hand, unlike the metro accommodating apparatus 5C, sincethe ATM access network accommodated IF of this embodiment 31 does notneed to execute flooding processing, loads can be reduced.

FIG. 13 is a flowchart of processing of the MPLS decapsulating andallocation unit of the first embodiment of the present invention.

On receiving an MPLS packet from the switch packet receiving unit 51,the MPLS decapsulating and allocation unit 52 executes relevantprocessing.

First, the MPLS decapsulating and allocation unit 52 selects a recordcorresponding to a received MPLS packet from the MPLS connection table53 (S191).

Specifically, it extracts a tunnel label value and a VC label value fromthe received MPLS packet. Next, it selects a record having a tunnellabel value 71 matching the extracted tunnel label value and a VC labelvalue 72 matching the extracted VC label value from the MPLS connectiontable 53.

Next, it determines whether a record corresponding to the received MPLSpacket has been selected from the MPLS connection table 53 (S192).

When a record corresponding to the received MPLS packet has not beenselected, it discards the received MPLS packet (S195).

On the other hand, when a record corresponding to the received MPLSpacket has been selected, it extracts a connection ID 73 and an upperlayer communication protocol type 74 from the selected record (S193).

Next, it deletes a tunnel label and a VC label from the received MPLSpacket. Thereby, it converts the received MPLS packet into the payloadof ATM cell, a TDM frame, or an Ethernet frame.

Next, it adds the extracted connection ID 73 to the start of the payloadof ATM cell, the TDM frame, or the Ethernet frame that are generated bythe conversion.

Next, it determines a generating unit corresponding to the extractedupper layer communication protocol type 74 from among the ATM bearergenerating unit 54A, the AAL1 generating unit 54B, and the AAL5generating unit 54C.

For example, when the extracted upper layer communication protocol type74 indicates “ATM bearer,” it determines the ATM bearer generating unit54A. When the extracted upper layer communication protocol type 74indicates “AAL1,” it determines AAL1 generating unit 54B. When theextracted upper layer communication protocol type 74 indicates “AAL5,”it determines AAL5 generating unit 54C.

Next, it transmits the payload of ATM cell, the TDM frame, or theEthernet frame that are added with the connection ID 73 to a determinedgenerating unit (S194).

For example, the MPLS decapsulating and allocation unit 52 transmits thepayload of ATM cell added with the connection ID 73 to the determinedATM bearer generating unit 54A. Moreover, it transmits a TDM frame addedwith the connection ID 73 to the determined AAL1 generating unit 54B. Ittransmits an Ethernet frame added with the connection ID 73 to thedetermined AAL5 generating unit 54C.

Then, it terminates the processing.

Thus, the MPLS decapsulating and allocation unit 52 determines an upperlayer communication protocol type of the received MPLS packet, based onthe tunnel label value and the VC label value of the received MPLSpacket. Therefore, one ATM access network accommodated IF can supportthree types of upper communication protocols the ATM bearer, AAL1, andAAL5.

FIG. 14 is a flowchart of processing of the ATM header generating unit56 of the embodiment of the present invention.

On receiving the payload of ATM cell from the scheduler 55, the ATMheader generating unit 56 executes relevant processing.

First, it extracts a connection ID from the received payload of ATMcell. Next, it selects a record having a connection ID 75 matching theextracted connection ID from the ATM header conversion table 57 (S201).

Next, it extracts VPI 76 and VCI 77 from the selected record (S202).

Next, it creates an ATM header by storing the extracted VPI and VCI inthe ATM header (S203). Next, it adds the created ATM header to thereceived payload of ATM cell. Thereby, the ATM header generating unit 56generates an ATM cell.

Next, it transmits the generated ATM cell to ATM cell transmitting unit58. Then, it terminates the relevant processing.

Thus, the ATM header generating unit 56 determines the VPI and VCI ofthe ATM header, based on the connection ID instead of informationcontained in the TDM frame or Ethernet frame. The connection ID isuniquely determined by the tunnel label and the VC label of an MPLSpacket converted into the TDM frame or Ethernet frame. However, theconnection ID may be uniquely determined by only the tunnel label of theMPLS packet instead of the tunnel label and the VC label of the MPLSpacket.

Therefore, the ATM access network accommodated IF 31, unlike the AAL1accommodating apparatus 4B2 shown in FIG. 2, does not store a timeslot—ATM header information correspondence table. The time slot—ATMheader information correspondence table is a table searching for ATMheader information containing VPI and VCI from time slot of TDM frame.Therefore, the time slot—ATM header information correspondence tableshows the correspondence between time slots of TDM frame and ATM headerinformation.

The ATM access network accommodated IF 31, unlike the AAL5 accommodatingapparatus 4C2 shown in FIG. 2, does not need to store the MACaddress—ATM header information correspondence table. The MAC address—ATMheader information correspondence table is a table for searching for theATM header information from a destination MAC address of Ethernet frame.Therefore, the MAC address—ATM header information correspondence tableshows the correspondence between MAC address and ATM header information.

The ATM access network accommodated IF of this embodiment 31 determinesATM header information based on a connection ID. Therefore, the ATMaccess network accommodated IF 31, unlike the metro accommodatingapparatus 5C shown in FIG. 2, does not execute MAC automatic learningprocessing. Moreover, the ATM access network accommodated IF 31, unlikethe metro accommodating apparatus 5C shown in FIG. 2, does not executeflooding processing.

FIG. 15 is an explanatory drawing of protocol stack of communicationconcerning TDM frame of the embodiment of the present invention.

On receiving a TDM frame from the user terminal 2, the AAL1accommodating apparatus 4B1 encapsulates the TDM frame received from theuser terminal 2 with the AAL1 format. Thereby, the AAL1 accommodatingapparatus 4B1 converts the received TDM frame into an AAL1 frame.

Next, the AAL1 accommodating apparatus 4B1 splits the AAL1 framegenerated by the conversion into ATM cell size, and adds an ATM header.Thereby, the AAL1 accommodating apparatus 4B1 converts the AAL1 frameinto an ATM cell. Then, it transmits the ATM cell generated by theconversion to the ATM access network 10.

On receiving the ATM cell from the ATM access network 10, the ATM accessnetwork accommodated IF 31 of the packet transfer apparatus 100 convertsthe received one or more ATM cells into an AAL1 frame. Next, itdecapsulates the AAL1 frame generated by the conversion. Thereby, theATM access network accommodated IF 31 converts the AAL1 frame into a TDMframe.

Moreover, the ATM access network accommodated IF 31 determines an MPLSlabel, based on the ATM header information of the received ATM cell.Then, it encapsulates the TDM frame generated by the conversion with thedetermined MPLS label. Thereby, it converts the TDM frame into an MPLSpacket.

The ATM access network accommodated IF 31 transmits the MPLS packetgenerated by the conversion to the packet switching metro area network30 via the switch 32 and the MPLS metro IF 9A.

The following describes communication concerning a TDM frame in anopposite direction.

The ATM access network accommodated IF 31 receives an MPLS packet fromthe packet switching metro area network 30 via the switch 32 and theMPLS metro IF 9A. Then, it determines an ATM header, based on the MPLSlabel of the received MPLS packet.

Next, it decapsulates the received MPLS packet. Thereby, it converts theMPLS packet into the TDM frame.

Next, it encapsulates the TDM frame generated by the conversion with theAAL1 format. Thereby, it converts the TDM frame into an AAL1 frame.

Next, it splits the AAL1 frame generated by the conversion into thepayload size of ATM cell. Thereby, it converts the AAL1 frame into thepayload of ATM cell.

Next, it adds the determined ATM header to the payload of ATM cellgenerated by the conversion. Thereby, it creates an ATM cell. Then, ittransmits the created ATM cell to the ATM access network 10.

The AAL1 accommodating apparatus 4B1 receives an ATM cell from the ATMaccess network 10. It converts the received one or more ATM cells intoan AAL1 frame. Next, it decapsulates the AAL1 frame generated by theconversion. Thereby, it converts the AAL1 frame into a TDM frame.

The AAL1 accommodating apparatus 4B1 transmits the TDM frame generatedby the conversion to the user terminal 2.

FIG. 16 is an explanatory drawing of protocol stack of communicationconcerning TDM frame in a telecommunications carrier's networkconstructed as shown in FIG. 2.

On receiving a TDM frame from the user terminal 2, the AAL1accommodating apparatus 4B1 encapsulates the TDM frame with the AAL1format. Thereby, the AAL1 accommodating apparatus 4B1 converts thereceived TDM frame into an AAL1 frame.

Next, it splits the AAL1 frame generated by the conversion into ATM cellsize, and adds an ATM header. Thereby, it converts the AAL1 frame intoan ATM cell. Then, it transmits the ATM cell generated by the conversionto the ATM access network 10.

On receiving an ATM cell from the ATM access network 10, the AAL1accommodating apparatus 4B2 converts the received one or more ATM cellsinto an AAL1 frame. Next, it decapsulates the AAL1 frame generated bythe conversion. Thereby, it converts the AAL1 frame into a TDM frame.Then, it transmits the TDM frame generated by the conversion to themetro accommodating apparatus 5B.

On receiving the TDM frame from the AAL1 accommodating apparatus 4B2,the metro accommodating apparatus 5B determines an MPLS label, based onthe time slot of the received TDM frame. Next, it encapsulates thereceived TDM frame with the determined MPLS label. Thereby, the ATMaccess network accommodated IF 31 converts the received TDM frame intoan MPLS packet.

The metro accommodating apparatus 5B transmits the MPLS packet generatedby the conversion to the packet switching metro area network 30.

Thus, the metro accommodating apparatus 5B determines an MPLS label,based on the time slot of the received TDM frame. Therefore, it musthave to store a time slot—MPLS label correspondence table showing thecorrespondence between the time slots of TDM frames and the identifiersof MPLS labels.

On the other hand, the ATM access network accommodated IF of thisembodiment 31 determines an MPLS label, based on the ATM headerinformation of a received ATM cell. Therefore, the ATM access networkaccommodated IF 31 does not need to store time slot MPLS labelcorrespondence table.

The following describes communication concerning a TDM frame in anopposite direction.

On receiving an MPLS packet from the packet switching metro area network30, the metro accommodating apparatus 5B decapsulates the received MPLSpacket. Thereby, the metro accommodating apparatus 5B converts the MPLSpacket into a TDM frame.

Next, it transmits the TDM frame generated by the conversion to the AAL1accommodating apparatus 4B2.

On receiving the TDM frame from the metro accommodating apparatus 5B,the AAL1 accommodating apparatus 4B2 determines an ATM header, based onthe time slot, of the received TDM frame. Next, it encapsulates' thereceived TDM frame with the AAL1 format. Thereby, the AAL1 accommodatingapparatus 4B2 converts the received TDM frame into an AAL1 frame.

Next, it splits the AAL1 frame generated by the conversion into thepayload size of ATM cell. Thereby, it converts the AAL1 frame into thepayload of ATM cell.

Next, it adds the determined ATM header to the payload of ATM cellgenerated by the conversion. Thereby, it creates an ATM cell. Then, ittransmits the created ATM cell to the ATM access network 10.

The AAL1 accommodating apparatus 4B1 receives an ATM cell from the ATMaccess network. Next, it converts the received one or more ATM cellsinto an AAL1 frame. Next, it decapsulates the AAL1 frame generated bythe conversion. Thereby, it converts the AAL1 frame into a TDM frame.

It transmits the TDM frame generated by the conversion to the userterminal 2.

Thus, the AAL1 accommodating apparatus 4B2 determines the ATM header,based on the time slot of the received TDM frame. Therefore, it musthave to store a time slot—ATM header information correspondence tableindicating the correspondence between the time shots of TDM frames andATM header information.

On the other hand, the ATM access network accommodated IF of thisembodiment 31 determines an ATM header, based on the tunnel label andthe VC label of a received MPLS packet. Therefore, the ATM accessnetwork accommodated IF 31 does not need to store the time slot—ATMheader information correspondence table.

FIG. 17 is an explanatory drawing of protocol stack of communicationconcerning Ethernet frame of the embodiment of the present invention.FIG. 18 is an explanatory drawing of communication concerning Ethernetframe of the embodiment of the present invention.

On receiving an Ethernet frame 81 from the user terminal 3, the AAL5accommodating apparatus 4C1 encapsulates the Ethernet frame 81 receivedfrom the user terminal 3 with the AAL5 format. Thereby, it converts thereceived Ethernet frame 81 into an AAL5 frame 82.

Next, it splits the AAL5 frame 82 generated by the conversion into ATMcell size, and adds an ATM header. Thereby, it converts the AAL5 frame82 into ATM cells 831, 832, and 833. Then, the AAL5 accommodatingapparatus 4C1 transmits the ATM cells 831, 832, and 833 generated by theconversion to the ATM access network 10.

The Ethernet frame 81 transmitted from the user terminal 3 is classifiedinto a user flow 85 according to a combination of a sender MAC addressand a destination MAC address. The user flow 85 is associated with VC(Virtual Channel) connection 86 in the AAL5 accommodating apparatus 4C1.The VC connection 86 is a minimum unit of the ATM connection. Forexample, one VC connection 86 is associated with one or more user flows85 that are inputted from an identical physical port and have anidentical destination. Furthermore, the VC connection 86 is associatedwith VP (Virtual Path) connection 87. The destination of an ATM cell isdetermined by these associations.

On receiving ATM cells 831, 832, and 833 from the ATM access network 10,the ATM access network accommodated IF 31 of the packet transferapparatus 100 converts the received ATM cells 831,832 and 833 into anAAL5 frame 82. Next, it decapsulates the AAL5 frame 82 generated by theconversion. Thereby, it converts the AAL5 frame 82 into an Ethernetframe 81.

Moreover, the ATM access network accommodated IF 31 determines an MPLSlabel, based on the ATM header information of the received ATM cells831, 832, and 833. Then, it encapsulates an Ethernet frame 81 generatedby the conversion with the determined MPLS label. Thereby, it convertsthe Ethernet frame 81 into an MPLS packet 84.

Then, it transmits the MPLS packet 84 generated by the conversion to thepacket switching metro area network 30 via the switch 32 and the MPLSmetro IF 9A.

The following describes communication concerning Ethernet frame in anopposite direction.

The ATM access network accommodated IF 31 receives an MPLS packet 84from the packet switching metro area network 30 via the switch 32 andthe MPLS metro IF 9A. Then, it determines an ATM header, based on theMPLS label of the received MPLS packet 84.

Next, it decapsulates the received MPLS packet 84. Thereby, it convertsthe MPLS packet 84 into an Ethernet frame 81.

Next, it encapsulates the Ethernet frame 81 generated by the conversionwith the AAL5 format. Thereby, it converts the Ethernet frame 81 into anAAL5 frame 82.

Next, it splits the AAL5 frame 82 generated by the conversion into thepayload size of ATM cell. Thereby, it converts the AAL5 frame into thepayload of ATM cell.

Next, it adds the determined ATM header to the payload of ATM cellgenerated by the conversion. Thereby, it creates ATM cells 831, 832, and833. Then, it transmits the created ATM cells 831, 832, and 833 to theATM access network 10.

On receiving the ATM cells 831, 832, and 833 from the ATM access network10, the AAL5 accommodating apparatus 4C1 converts the received ATM cells831; 832, and 833 into an AAL5 frame 82. Next, it decapsulates the AAL5frame 82 generated by the conversion. Thereby, it converts the AAL5frame 82 into an Ethernet frame 81.

Then, it transmits the Ethernet frame 81 generated by the conversion tothe user terminal 3.

FIG. 19 is an explanatory drawing of protocol stack of communicationconcerning Ethernet frame in the telecommunications carrier's networkconstructed as shown in FIG. 2. FIG. 20 is an explanatory drawing ofcommunication concerning Ethernet frame in the telecommunicationscarrier's network constructed as shown in FIG. 2.

On receiving an Ethernet frame 21 from the user terminal 3, the AAL5accommodating apparatus 4C1 encapsulates the Ethernet frame 21 receivedfrom the user terminal 3 with the AAL5 format. Thereby, it converts thereceived Ethernet frame 21 into an AAL5 frame 22.

Next, it splits the AAL5 frame 22 generated by the conversion into ATMcell size, and adds an ATM header. Thereby, it converts the AAL5 frame22 into ATM cells 231, 232, and 233. Then, it transmits the ATM cells231, 232, and 233 generated by the conversion to the ATM access network10.

The Ethernet frame 81 transmitted from the user terminal 3 is classifiedinto a user flow 25 according to a combination of a sender MAC addressand a destination MAC address. The user flow 25 is associated with a VCconnection 26 in the AAL5 accommodating apparatus 4C1. The VC connection26 is a minimum unit of ATM connection. For example, one VC connectionis associated with one or more user flows 25 that are inputted from anidentical physical port and have an identical destination. Furthermore,the VC connection 26 is associated with VP (Virtual Path) connection 27.The destination of an ATM cell is determined by these associations.

On receiving ATM cells 231, 232, and 233 from the ATM access network 10,the AAL5 accommodating apparatus 4C2 converts the received ATM cells231, 232, and 233 into an AAL5 frame 22. Next, it decapsulates the AAL5frame 22 generated by the conversion. Thereby, the AAL1 accommodatingapparatus 4B2 converts the AAL5 frame 22 into an Ethernet frame 21.Then, the AAL5 accommodating apparatus 4C2 transmits the Ethernet frame21 generated by the conversion to the metro accommodating apparatus 5C.

On receiving the Ethernet frame 21 from the AAL1 accommodating apparatus4B2, the metro accommodating apparatus 5C determines an MPLS label,based on the destination MAC address of the received Ethernet frame 21.Next, it encapsulates the received Ethernet frame 21 with the determinedMPLS label. Thereby, the ATM access network accommodated IF 31 convertsthe received Ethernet frame 21 into an MPLS packet 24.

The metro accommodating apparatus 5C transmits the MPLS packet 24generated by the conversion to the packet switching metro area network30.

Thus, the metro accommodating apparatus 5C determines the MPLS label,based on the destination MAC address of the received Ethernet frame.Therefore, it must store a MAC address—MPLS label correspondence tableshowing correspondence between the destination MAC addresses of Ethernetframes and the identifiers of MPLS labels.

On the other hand, the ATM access network accommodated IF 31 of thisembodiment determines the MPLS label, based on the ATM headerinformation of received ATM cell. Therefore, it does not need to storethe MAC address—MPLS label correspondence table. Accordingly, it doesnot need to execute the MAC learning processing.

The ATM access network accommodated IF 31 does not need to select adifferent MPLS label for each user flow. Therefore, it does not need todetermine a user flow, based on the MAC address and the like of Ethernetframe. Furthermore, a change in the number of user flows exerts noinfluence on the ATM access network accommodated IF 31.

The following describes communication concerning Ethernet frame in anopposite direction.

On receiving an MPLS packet 24 from the packet switching metro areanetwork 30, the metro accommodating apparatus 5C decapsulates thereceived MPLS packet 24. Thereby, it converts the MPLS packet 24 into anEthernet frame 21.

Next, it transmits the Ethernet frame 21 generated by the conversion tothe AAL5 accommodating apparatus 4C2.

On receiving the Ethernet frame 21 from the metro accommodatingapparatus 5C, the AAL5 accommodating apparatus 4C2 determines an ATMheader, based on the destination MAC address of the received Ethernetframe 21.

Next, it encapsulates the received Ethernet frame 21 with the AAL5format. Thereby, it converts the received Ethernet frame 21 into an AAL5frame 22.

Next, it splits the AAL5 frame 22 generated by the conversion into thepayload size of ATM cell. Thereby, it converts the AAL5 frame into thepayload of ATM cell.

Next, it adds the determined ATM header to the payload of ATM cellgenerated by the conversion. Thereby, it creates ATM cells 231, 232, and233. Then, it transmits the created ATM cells 231, 232, and 233 to theATM access network 10.

The AAL5 accommodating apparatus 4C1 receives ATM cells 231, 232, and233 from the ATM access network 10. Next, it converts the received ATMcells 231, 232, and 233 into an AAL5 frame 22. Next, it decapsulates theAAL5 frame 22 generated by the conversion. Thereby, it converts the AAL5frame 22 into an Ethernet frame 21.

Then, it transmits the Ethernet frame 21 generated by the conversion tothe user terminal 3.

Thus, the AAL5 accommodating apparatus 4C2 determines an ATM header,based on the destination MAC address of the received Ethernet frame.Therefore, it must store the MAC address—ATM header informationcorrespondence table showing the correspondence between the destinationMAC addresses of Ethernet frames and ATM header information.

On the other hand, the ATM access network accommodated IF 31 of thisembodiment determines an ATM header, based on the tunnel label and VClabel of a received MPLS packet. Therefore, it does not need to storethe MAC address—ATM header information correspondence table.

What is claimed is:
 1. A packet transfer system comprising: a firstpacket transfer apparatus in a first network operated with a firstcommunication protocol; and a second packet transfer apparatus in thefirst network operated with the first communication protocol, whereinthe first packet transfer apparatus comprises: a first interface thatreceives a second communication protocol packet from a second networkoperated with a second communication protocol, the second communicationprotocol packet being generated by a third communication protocolpacket, converts the second communication protocol packet into the thirdcommunication protocol packet with terminating the second communicationprotocol, and converts the third communication protocol packet withterminating the second communication protocol into a first communicationprotocol packet by adding a header of the first communication protocolpacket, and a second interface that sends the first communicationprotocol packet into the first network, and wherein the second packettransfer apparatus comprises: a third interface that receives the firstcommunication protocol packet from the first network, and a fourthinterface that converts the first communication protocol packet into thethird communication protocol packet, and sends the third communicationprotocol packet to a third network.
 2. The packet transfer systemaccording to claim 1, wherein the first interface converts the thirdcommunication protocol packet into the first communication protocolpacket by adding the header of the first communication protocol packetwhich is generated based on destination information of the firstcommunication protocol packet corresponding to destination informationof a header of the received second communication protocol packet to thethird communication protocol packet.
 3. The packet transfer systemaccording to claim 2, wherein the first packet transfer apparatusfurther comprises first destination information containing acorrespondence between the destination information of the secondcommunication protocol packet and the destination information of thefirst communication protocol packet, and the first interface identifiesthe destination information of the second communication protocol packetcorresponding to the destination information of the received firstcommunication protocol packet based on the first destinationinformation.
 4. The packet transfer system according to claim 1, whereinthe first interface converts the second communication protocol packetinto the third communication protocol with terminating the secondcommunication protocol by assembling a plurality of second communicationpackets, and discarding a header of the received second communicationprotocol packet, the third communication protocol being encapsulatedwith the header of the second communication protocol.
 5. The packettransfer system according to claim 1, wherein the second interfacereceives a first communication packet from the first network the firstcommunication packet is generated by a conversion of a thirdcommunication protocol packet, and wherein the first interface convertsthe first communication packet into a plurality of second communicationpacket by discarding header information of the second communicationpacket, and dividing the first communication packet into the pluralityof second communication protocol packets, and transmits the plurality ofsecond communication protocol packets to the second network.
 6. Thepacket transfer system according to claim 1, wherein the first interfaceconverts the received second communication protocol packet to the thirdcommunication protocol packet based on a type of upper communicationprotocol identified by the destination information of the receivedsecond communication protocol packet.
 7. The packet transfer systemaccording to claim 6, wherein the first destination information furtherincludes a correspondence between the destination information of thesecond communication protocol packet and the type of upper communicationprotocol, and the first interface converts the received secondcommunication protocol packet to the third communication protocol packetbased on the first destination information.
 8. The packet transfersystem according to claim 6, wherein the upper communication protocol isAAL1, AAL5, and ATM bearer, and the first packet transfer apparatusreads out preferentially the third communication protocol packet whoseupper communication protocol is AAL1.
 9. A method for packet transferbetween a first network operated with a first communication protocol anda second network operated with a second communication protocol, themethod comprising: receiving a second communication protocol packet fromthe second network at a first packet transfer apparatus, the secondcommunication protocol packet being generated by a third communicationprotocol packet; converting the second communication protocol packetinto the third communication protocol with terminating the secondcommunication protocol at the first packet transfer apparatus;converting the third communication protocol packet with terminating thesecond communication protocol into a first communication protocol packetby adding a header of the first communication protocol packet at a firstcommunication apparatus; sending the first communication protocol packetinto the first network; receiving the first communication protocolpacket from the first network at a second packet transfer apparatus;converting the first communication protocol packet into the thirdcommunication protocol packet at the second packet transfer apparatus;and sending the third communication protocol packet to a third networkat the second packet transfer apparatus.
 10. The method according toclaim 9, further comprising: converting the third communication protocolpacket into the first communication protocol packet by adding the headerof the first communication protocol packet which is generated based ondestination information of the first communication protocol packetcorresponding to destination information of a header of the receivedsecond communication protocol packet to the third communication protocolpacket at the first packet transfer apparatus.
 11. The method accordingto claim 9, further comprising: converting the second communicationprotocol packet into the third communication protocol with terminatingthe second communication protocol at the first packet transfer apparatusby assembling a plurality of second communication packets, anddiscarding a header of the received second communication protocolpacket, the third communication protocol being encapsulated with theheader of the second communication protocol.
 12. The method according toclaim 9, further comprising: receiving a first communication packet fromthe first network at the first packet transfer apparatus, the firstcommunication packet being generated by a conversion of a thirdcommunication protocol packet, and converting the first communicationpacket into a plurality of second communication packet at the firstpacket transfer apparatus by discarding header information of the secondcommunication packet, and dividing the first communication packet intothe plurality of second communication protocol packets, and transmittingthe plurality of second communication protocol packets to the secondnetwork at the first packet transfer apparatus.
 13. A packet transferapparatus in a first network operated with a first communicationprotocol comprising: a first interface that receives a secondcommunication protocol packet from a second network operated with asecond communication protocol, the second communication protocol packetis generated by a third communication protocol packet, converts thesecond communication protocol packet into the third communicationprotocol packet with terminating the second communication protocol, andconverts the third communication protocol packet with terminating thesecond communication protocol into a first communication protocol packetby adding a header of the first communication protocol packet, and asecond interface that sends the first communication protocol packet intothe first network, wherein the first network is connected to a thirdnetwork and the first communication packet is sent out the third networkafter converting into a third communication protocol packet.
 14. Thepacket transfer apparatus according to claim 13, wherein the firstinterface converts the third communication protocol packet into thefirst communication protocol packet by adding the header of the firstcommunication protocol packet which is generated based on destinationinformation of the first communication protocol packet corresponding todestination information of a header of the received second communicationprotocol packet to the third communication protocol packet.
 15. Thepacket transfer apparatus according to claim 14, further comprising:first destination information containing a correspondence between thedestination information of the second communication protocol packet andthe destination information of the first communication protocol packet,wherein the first interface identifies the destination information ofthe second communication protocol packet corresponding to thedestination information of the received first communication protocolpacket based on the first destination information.
 16. The packettransfer apparatus according to claim 13, wherein the first interfaceconverts the second communication protocol packet into the thirdcommunication protocol with terminating the second communicationprotocol by assembling a plurality of second communication packets, anddiscarding a header of the received second communication protocolpacket, the third communication protocol being encapsulated with theheader of the second communication protocol.
 17. The packet transferapparatus according to claim 13, wherein the second interface receives afirst communication packet from the first network and the firstcommunication packet is generated by a conversion of a thirdcommunication protocol packet, and the first interface converts thefirst communication packet into a plurality of second communicationpacket by discarding header information of the second communicationpacket, dividing the first communication packet into the plurality ofsecond communication protocol packets, and transmits the plurality ofsecond communication protocol packets to the second network.
 18. Thepacket transfer apparatus according to claim 13, wherein the firstinterface converts the received second communication protocol packet tothe third communication protocol packet based on a type of uppercommunication protocol identified by the destination information of thereceived second communication protocol packet.
 19. The packet transferapparatus according to claim 18, wherein the first destinationinformation further includes a correspondence between the destinationinformation of the second communication protocol packet and the type ofupper communication protocol, and the first interface converts thereceived second communication protocol packet to the third communicationprotocol packet based on the first destination information.
 20. Thepacket transfer apparatus according to claim 18, wherein the uppercommunication protocol is AAL1, AAL5, and ATM bearer, and the firstpacket transfer apparatus reads out preferentially the thirdcommunication protocol packet whose upper communication protocol isAAL1.